puppies staying with mother?

Question
My German Shepherd had six puppies.  Four of them went back to the
breeder.  Two of them I have.  A male and a female, 9 weeks this Thursday.  
Here is the problem.  I started taking them outside for daily walks, getting
them use to the outdoors.  The bitch is in a very large pen.  Half concrete and
half sand.  I want to start putting the puppies in the pen with the mother.  
However when I do so, the mother plays very rough with them.  Whenever
they try to make a move she goes after them.  She bites their noses.  And
what I mean by that is that she puts her whole mouth over their mouth.  It's
very strange but she constantly does that.  I was going to gradually put the
pups in with her starting out with an hour at a time.  But it seems I can't even
leave them in there with her for 15 minutes.  I'm afraid she will do harm to
them.  Is this behavior normal and do you have any suggestions as to what I
should do?
Thank you for your time.  

Answer
At this age, it is pretty unlikely that the bitch would really hurt her own puppies. Generally, it is a case of "mother knows best" when it comes to puppyrearing. What she is doing is telling them who is boss, as the muzzle is an area of dominance, just as is the top of the shoulders. These puppies must be somewhat dominant, and she is telling them to behave or else.

I once took a trip with a litter of puppies and their mother, and at every stop, the bitch would pin one specific puppy to the ground and do it just about every time the puppy tried to move around the exercise pen. I never saw any sign of dominance from that puppy, but her mother did. When I returned home, I instructed the new owners how to manage this puppy so that it would grow up into a well-behaved dog (which it did).

Pay attention to what your dog does; she is telling you how to raise those puppies. I highly recommend "Long Downs" for dominant puppies. http://www.volhard.com/general/artbywv.htm#tnw

And be sure you continue with the people socialization with those puppies. Get them out and introduce them to many different situations and people. I highly recommend the book, "How to Raise a Puppy You Can Live With", by Rutherford and Neil.